1. Field of the Invention
The present invention relates to a printing device for printing bar codes which can be omnidirectionally read out in an automatic manner by means of an optical reader, and more particularly to improvements in a bar code printing device which is used with a portable label printing and applying machine or a table type automatic label printer, or the like, so that it can print bar code on a series of composite labels each composed of a label and a sheet of backing paper.
2. Description of the Prior Art
Representative printing devices of this kind are disclosed in U.S. Pat. Nos. 4,018,157 and 4,155,302, both by the inventor hereof.
Recently, the so-called "POS" (Point-of-Sale) system has been put into practice in large size supermarkets. In one type of bar code, as shown on label L in FIG. 1 of the drawings hereof, one numeral is composed, in combination, of two dark bars having a height of 14 mm and two light spaces, both of which are arranged in parallel to constitute one character (or seven modules). The character thus constituted is required to have a width of 2.31 mm with an allowance of .+-.0.101 mm.
The bar code printing device has a plurality of bar code rings juxtaposed side by side on a common axis of rotation. Each of the bar code type rings is formed with a set of numerals. Each numeral is composed of dark and light bars having sizes selected to correspond to the particular numeral. The bar code numeral is made highly accurate.
However, there are problems in establishing precise gaps between the type rings, which are axially juxtaposed. Even the one light space which is left at one end of each bar code type ring plays an important role as a symbol. Therefore, an unnecessary gap between two adjacent type rings would cause an incorrect number to be read out by the optical reader. On the other hand, when the respective bar code type rings are pushed together in fixed contact, a desired ring cannot be selectively turned to change the numeral thereon.